The invention relates to an improved fuel injector which effectively controls fuel metering.
In most fuel supply systems applicable to internal combustion engines, fuel injectors are used to direct fuel pulses into the engine combustion chamber. A commonly used injector is a closed-nozzle injector which includes a nozzle assembly having a spring-biased nozzle valve element positioned adjacent the nozzle orifice for resisting blow back of exhaust gas into the pumping or metering chamber of the injector while allowing fuel to be injected into the cylinder. The nozzle valve element also functions to provide a deliberate, abrupt end to fuel injection thereby preventing a secondary injection which causes unburned hydrocarbons in the exhaust. The nozzle valve is positioned in a nozzle cavity and biased by a nozzle spring to block fuel flow through the nozzle orifices. In many fuel systems, when the pressure of the fuel within the nozzle cavity exceeds the biasing force of the nozzle spring, the nozzle valve element moves outwardly to allow fuel to pass through the nozzle orifices, thus marking the beginning of injection.
In another type of system, such as disclosed in U.S. Pat. No. 5,819,704, the beginning of injection is controlled by a servo-controlled needle valve element. The assembly includes a control volume positioned adjacent an outer end of the needle valve element, a drain circuit for draining fuel from the control volume to a low pressure drain, and an injection control valve positioned along the drain circuit for controlling the flow of fuel through the drain circuit so as to cause the movement of the needle valve element between open and closed positions. Opening of the injection control valve causes a reduction in the fuel pressure in the control volume resulting in a pressure differential which forces the needle valve open, and closing of the injection control valve causes an increase in the control volume pressure and closing of the needle valve.
U.S. Pat. No. 5,862,793 discloses an injection valve arrangement which includes a solenoid actuated control valve for controlling drain flow from a chamber, a poppet type needle valve movable outwardly to permit injection and an auxiliary valve positioned between the chamber and the needle valve for controlling high pressure fuel flow to a needle control chamber positioned adjacent an outer end of the needle valve. The opening of the control valve causes the opening of the auxiliary valve which then causes the opening of the needle valve. However, the auxiliary valve opens to allow high pressure fuel to enter the needle control chamber thereby increasing the pressure in the needle control chamber. The high pressure in the needle control chamber acts on the needle valve to move the needle valve outwardly into an open position to cause injection.
There is still a need for a simple, improved fuel injector which is capable of effectively controlling fuel metering while handling high fuel injection flow rates using conventional actuators.
It is, therefore, one object of the present invention to overcome the deficiencies of the prior art and to provide a fuel injector which better enables large engines to meet future diesel engine exhaust emission requirements while minimizing fuel consumption.
Another object of the present invention is to provide a fuel injector which can be effectively used in high horsepower engines in combination with actuator assemblies used on smaller engines/injectors.
Yet another object of the present invention is to provide a fuel injector for larger engines which avoids larger and higher energy consuming actuators and thus minimizes injector packaging and costs.
Still another object of the present invention is to provide a fuel injector having a primary control valve and an intermediate control valve wherein oscillations of the intermediate valve are minimized.
These and other objects are achieved by providing a fuel injector for injecting fuel at high pressure into the combustion chamber of an engine, comprising an injector body containing an injector cavity and an injector orifice communicating with one end of the injector cavity to discharge fuel into the combustion chamber. The injector also includes a nozzle valve element positioned in one end of the injector cavity adjacent the injector orifice and movable between an open position in which fuel may flow through the injector orifice into the combustion chamber and a closed position in which fuel flow through the injector orifice is blocked. The injector also includes a first control volume positioned to receive a pressurized supply of fuel, a drain circuit for draining fuel from the first control volume to a low pressure drain and a first valve seat positioned along the drain circuit. A first injection control valve is also positioned along the drain circuit to control fuel flow from the first control volume and includes a reciprocally mounted control valve member movable between an open position permitting flow through the drain circuit and a closed position in sealing abutment against the first valve seat to block flow through the drain circuit. A second control volume is also provided and positioned adjacent an outer end of the nozzle valve element to receive a pressurized supply of fuel while the drain circuit is positioned to drain fuel from the second control volume to the low pressure drain. A second valve seat is positioned along the drain circuit along with a second injection control valve to control fuel flow from the second control volume. The second injection control valve includes a reciprocally mounted control valve member movable between an open position permitting flow through the drain circuit to cause a decrease in fuel pressure in the second control volume and movement of the nozzle valve element into the open position, and a closed position in sealing abutment against the second valve seat to block flow through the drain circuit to cause an increase in fuel pressure in the second control volume and movement of the nozzle valve element into the closed position. Movement of the first injection control valve into the open position causes a decrease in fuel pressure in the first control volume thereby causing movement of the second injection control valve into the open position.
The first injection control valve may include a solenoid actuator assembly while the second injection control valve is spring biased into the closed position. A high pressure chamber may be positioned around the second injection control valve axially between the first injection control valve and the second control volume. The second injection control valve includes a large diameter portion positioned axially between the first control volume and the high pressure chamber, and a small diameter portion having an outer diameter smaller than the large diameter portion and positioned axially between the high pressure chamber and the second control volume. The second injection control valve includes a bias spring positioned in the high pressure chamber for biasing the second injection control valve into the closed position. The nozzle valve element may include an outer diameter greater than the largest outer diameter of the second injection control valve member. The nozzle valve element moves toward the second injection control valve into the open position. A bias spring for biasing the nozzle valve element into the closed position may be provided. A spring chamber containing the nozzle valve bias spring may be provided along with a high pressure fuel supply circuit including at least a portion of the spring chamber. A high pressure fuel supply circuit may also include at least a portion of the high pressure chamber.